In a high side hermetic rolling piston or fixed vane compressor the interior of the shell and the oil sump are at discharge pressure. The piston, cylinder or crankcase and vane are located between the pump end bearing and the motor end bearing with the pump end bearing, typically, being in contact with the oil sump. The vane reciprocates in a slot in the cylinder as it tracks the eccentric piston. While one end of the vane extends through the slot in the cylinder into the cavity and reciprocates in the slot as it tracks the piston, the other end is reciprocating in a spring chamber containing a spring which provides the biasing force keeping the vane in contact with the piston. At high speed, 5400-7200 rpm, the vane motion in the spring chamber behaves as a positive displacement oil pump. Independent of whether or not the vane is required as an oil pump, fluid communication with the spring chamber must be provided. A trapped volume subjected to an increase in the volume of the chamber will reduce the pressure in the chamber thereby opposing the spring which tends to bias the vane into increasing the volume. If a trapped volume contains oil or other incompressible fluids it will tend to act as a dashpot and will act with the spring to oppose movement of the vane into the spring chamber. A spring chamber extending through the crankcase has been used to avoid these problems.
A problem was noted in variable speed rotary compressors at a shaft speed of 90-120 Hz or 5400-7200 rpm. The problem was due to lubrication failure. The use of a sight glass determined that oil was being pumped out of the sump resulting in an inadequate amount of lubrication being available. The reduced amount of lubricant made bearings more prone to failure from refrigerant slugs as the refrigerant can more readily wash out the oil.